Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rex protein, the posttranscriptional regulator of human T-cell leukemia virus type I (HTLV-I), is required for the control of viral structural protein expression and virus replication. Rex is a phosphoprotein found predominantly in the cell nucleolus, whose function is thought to be regulated by its nucleolar localization and phosphorylation. Therefore, we investigated the in vivo phosphorylation of Rex protein in more detail. Phosphorylation of Rex occurred in all HTLV-I-infected cell lines examined in vivo, primarily at serine residues and to a very small extent at threonine residues. Treatment of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) led to significant but transient enhancement of the incorporation of [32P]orthophosphate into Rex protein. N-terminal truncation of Rex protein abolished TPA-dependent phosphorylation. Chymotryptic digestion of phosphorylated Rex yielded two phosphopeptides. In vivo phosphorylation sites were identified as serine residues 70 and 177 and threonine residue 174. Serine 70 was a TPA-dependent phosphorylation site within a regulatory domain. We have already shown that the protein kinase C inhibitor H-7 (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine) specifically blocked accumulation of viral unspliced gag-pol mRNA. Therefore, the phosphorylation at serine 70 may be involved in the regulation of Rex function in response to extracellular stimuli.
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PMID:Phosphorylation of the Rex protein of human T-cell leukemia virus type I. 140 May 9

Humanized IgG1 M195 (HuG1-M195), a complementarity determining region-grafted recombinant monoclonal antibody, is reactive with CD33, an antigen expressed on myelogenous leukemia cells. M195 is in use in trials for the therapy of acute myelogenous leukemia. Since biological activity of IgG may depend, in part, on multimeric Fab and Fc clustering, homodimeric forms of HuG1-M195 were constructed by introducing a mutation in the gamma 1 chain CH3 region gene to change a serine to a cysteine, allowing interchain disulfide bond formation at the COOH terminal of the IgG. Despite similar avidity, the homodimeric IgG showed a dramatic improvement in the ability to internalize and retain radioisotope in target leukemia cells. Moreover, homodimers were 100-fold more potent at complement-mediated leukemia cell killing and antibody-dependent cellular cytotoxicity using human effectors. Therefore, genetically engineered multimeric constructs of IgG may have advantages relative to those forms that are found naturally.
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PMID:Engineered humanized dimeric forms of IgG are more effective antibodies. 140 60

Bistratene A, a polyether toxin isolated from the colonial ascidian Lissoclinum bistratum, causes incomplete differentiation of human leukemia (HL-60) cells apparently through a mechanism not involving protein kinase C. In view of the importance of phosphorylation/dephosphorylation in cellular growth and differentiation we have investigated protein phosphorylation in these cells following exposure to bistratene A, using two-dimensional polyacrylamide gel electrophoresis. Marked increases in the phosphorylation of a protein of 20 kDa, pl 6.7, and a basic protein of 25 kDa were observed after incubation with bistratene A. A comparison was made with cells treated with 12-O-tetradecanoylphorbol 13-acetate and bryostatin 5. While changes in phosphorylation patterns were observed with these two compounds, the 20 kDa and 25 kDa proteins did not undergo phosphorylation changes. The 20 kDa protein was induced rapidly by very low concentrations of bistratene A reaching near maximal levels with 10 nM at 15 min exposure. This protein was found to be localised to the cytoplasm. Phosphoaminoacid analysis demonstrated that the majority of 32P was present in serine and tyrosine residues. The increased phosphorylation of the 20 kDa protein appeared to be due to hyperphosphorylation of existing protein although there was some increase in the amount of the protein. These results suggest that bistratene A will be a useful tool with which to investigate cellular differentiation mechanisms.
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PMID:Bistratene A: a novel compound causing changes in protein phosphorylation patterns in human leukemia cells. 142 68

We have made 47 mutations that span the length of the human T-cell leukemia virus type I (HTLV-I) Tax open reading frame. Of the 47 mutations, 38 were substitutions of single amino acids, 5 were missense changes in two or more amino acids, and 4 were deletions. A subset of these mutations includes individual changes of all 26 naturally occurring serines to alanines. By assaying each mutant protein separately on the HTLV-I long terminal repeat (LTR) and the human immunodeficiency virus type 1 (HIV-1) LTR in parallel, we were able to identify regions of Tax selectively necessary for each promoter. A small region in the carboxyl terminus, amino acids 315 to 325, was found to be selectively important for activation of the HTLV-I LTR. Three changes at serine 113, serine 160, and serine 258 were found to specifically affect function on the HIV-1 LTR. Surprisingly, we found that the great preponderance of missense changes (32 of 42) in Tax did not affect function.
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PMID:Mutational analysis of human T-cell leukemia virus type I Tax: regions necessary for function determined with 47 mutant proteins. 143 11

We have purified a 30-kDa serine protease (designated RNK-Met-1) from the granules of the rat large granular lymphocyte leukemia cell line (RNK-16) that hydrolytically cleaves model peptide substrates after methionine, leucine, and norleucine (Met-ase activity). Utilizing molecular sieve chromatography, heparin-agarose, chromatography, and reverse-phase high pressure liquid chromatography, RNK-Met-1 was purified to homogeneity and 25 NH2-terminal amino acids were sequenced. By using the polymerase chain reaction, oligonucleotide primers derived from amino acids at position 14-25 and from a downstream active site conserved in other serine protease genes were used to generate a 534-base pair cDNA clone encoding a novel serine protease from RNK-16 mRNA. This cDNA clone was used to isolate a full-length 867-base pair RNK-Met-1 cDNA from an RNK-16 lambda-gt11 library. The open reading frame predicts a mature protein of 238 amino acids with two potential sites for N-linked glycosylation. The cDNA also encodes a leader peptide of at least 20 amino acids. The characteristic Ile-Ile-Gly-Gly amino acids of the NH2 terminus and the His, Asp, and Ser residues that form the catalytic triad of serine proteases were both conserved. The amino acid sequence has less than 45% identity with any other member of the serine protease family, indicating that RNK-Met-1 is distinct and may itself represent a new subfamily of serine proteases. Northern blot analysis of total cellular RNA detected a single 0.9-kilobase mRNA in the in vitro and in vivo variants of RNK-16 and in spleen-derived plastic-adherent rat lymphokine-activated killer cells. RNK-Met-1 mRNA was not detectable in freshly isolated rat splenocytes, thymocytes, brain, colon, and liver or activated nonadherent rat splenocytes and thymocytes. These data indicate that RNK-Met-1 is a serine protease with unique activity that is expressed in the granules of large granular lymphocytes.
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PMID:Purification and cloning of a novel serine protease, RNK-Met-1, from the granules of a rat natural killer cell leukemia. 144 89

Pharmacologic differentiation of the promyelocytic leukemia HL60 is associated with an increase in cellular tyrosine phosphatase activity. We asked (a) if this increase might, at least in part, be due to changes in a transmembranous protein-tyrosine phosphatase, CD45; and (b) if CD45 changes similarly in other differentiating leukemias. Differentiation of HL60, several chronic myelogenous leukemias, a monocytic leukemia (THP-1), and a monoblastoid leukemia (U-937) could be induced by phorbol ester, 1,25-dihydroxy vitamin D3, dimethyl sulfoxide, or cyclic AMP analogues. This differentiation was associated with a marked increase in (a) total cellular tyrosine phosphatase activity (2-4-fold as measured by the ability to dephosphorylate a tyrosine-phosphorylated peptide); (b) CD45-specific tyrosine phosphatase activity (2-4-fold); (c) CD45 cell surface expression by flow cytometry (2-5-fold); (d) synthesis of both exon B-dependent M(r) 205,000 and exon ABC- M(r) 185,000 CD45 proteins, as revealed by immunoprecipitation with antisera specific for CD45 isoforms. Both isoforms have enhanced electrophoretic mobility when isolated from the differentiated cells. This enhanced mobility did not appear to be due to decreased stoichiometry of CD45 phosphorylation on serine/threonine residues. Interestingly, 12-O-tetradecanoylphorbol-13-acetate transiently reduced CD45 protein-tyrosine phosphatase activity in the chronic myelogenous leukemia cell RWLeu4 without altering the CD45 amount (as measured by cell surface immunofluorescence). Modulation of CD45 tyrosine phosphatase activity (and protein levels) may play a role in differentiation or in maintaining cells in a nonproliferative state or may represent a phenotypic marker of differentiation.
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PMID:Differentiation-induced changes in protein-tyrosine phosphatase activity and commensurate expression of CD45 in human leukemia cell lines. 153 52

We report the independent cloning of the cDNA for CD31, a recently described cell adhesion molecule of the immunoglobulin gene superfamily present on platelets, granulocytes, monocytes, lymphocytes, and endothelial cells. Northern analysis revealed three major mRNA transcripts in Jurkat (a human T cell line) and K562 and HEL (leukemia cell lines) cells with an additional 5.3-kilobase transcript seen in cultured human umbilical vein endothelial cells. Following T cell activation, CD31 mRNA was down-regulated by Northern analysis, and decreased CD31 protein expression was confirmed by immunoblots. The down-regulation of CD31 was partially mediated by decreased transcription as demonstrated by nuclear run-on studies. CD31 became rapidly phosphorylated in platelets, Jurkat cells, and endothelial cells after cell activation. We were unable to demonstrate the presence of a phosphotyrosine in CD31 using monoclonal and polyclonal phosphotyrosine antibodies. In addition, CD31 phosphorylation in platelets was induced by phorbol ester and was blocked by staurosporin, a protein kinase C inhibitor, suggesting that CD31 phosphorylation is mediated by protein kinase C and involves serine and/or threonine residues. The phosphorylation of CD31 following cell activation may modulate its cellular adhesiveness, and the down-regulation of its expression may serve to impart target specificity and to localize effector lymphocytes to areas of inflammation.
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PMID:The cell adhesion molecule CD31 is phosphorylated after cell activation. Down-regulation of CD31 in activated T lymphocytes. 154 7

The Rex protein of human T-cell leukemia virus types I (HTLV-I) and II (HTLV-II) regulates the expression of the viral structural genes and is critical for viral replication. Rex acts by specifically binding to RNAs containing sequences of the R region of the 5' long terminal repeat. Two forms of Rex detected in HTLV-II-infected cells, p26rex and p24rex, differ in the extent of serine phosphorylation. Two-dimensional phosphopeptide analysis indicates that p26rex is extensively phosphorylated at multiple sites. Using a sensitive immunobinding assay, we show that the phosphorylation state of Rex determines the efficiency of binding of Rex to HTLV-II target RNAs. Thus, the phosphorylation state of Rex in the infected cell may be a switch that determines whether virus exists in a latent or productive state. These studies also suggest that phosphorylation of RNA-binding regulatory proteins is a more general mechanism of gene regulation.
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PMID:Phosphorylation regulates RNA binding by the human T-cell leukemia virus Rex protein. 160 46

The knowledge about the differentiation of basophilic leukocytes is fragmentary. This report discusses a detailed phenotypic characterization of molecular markers for hematopoietic differentiation in a basophilic leukemia cell line, KU812. The expression of markers for lymphoid, erythroid, neutrophil, eosinophil, monocytic, megakaryocytic, mast cell and basophil differentiation was analyzed at the mRNA level by Northern blots in the KU812 cells, and for reference, in a panel of human cell lines representative of the different hematopoietic differentiation lineages. KU812 was found to express a number of mast cell and basophil-related proteins, i.e. mast cell tryptase, mast cell carboxypeptidase A, high-affinity immunoglobulin (IgE) receptor alpha and gamma chains and the core protein for heparin and chondroitin sulphate synthesis. We found no expression of a number of monocyte/-macrophage or neutrophil leukocyte markers except for lysozyme. From earlier studies, it has been shown that lysozyme is not expressed in murine mucosal mast cell lines. This finding, together with the expression of the mast cell carboxypeptidase in KU812 might distinguish the phenotype of this cell line from that typical of mucosal mast cell lines in rodents. We found a low level of expression of the eosinophil and basophil marker, major basic protein, which might indicate a relationship between basophils and eosinophils. No expression is, however, detected with the eosinophil-specific markers eosinophil cationic protein, eosinophil-derived neurotoxin or eosinophil peroxidase. We also report an extensive screening for inducers of basophilic differentiation of the KU812 cells. The most efficient protocol of induction included serum starvation which led to a dramatic increase in a number of markers specific for mast cells and basophils such as tryptase, carboxypeptidase A and the heparin core protein. Finally, diisopropylfluorophosphate analysis of total protein extracts from KU812 show four labeled protein bands with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that this cell line expresses at least three previously undescribed serine proteases of which one or more could be a potential basophil-specific marker(s).
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PMID:Phenotypic characterization of KU812, a cell line identified as an immature human basophilic leukocyte. 163 3

The binding of haemopoietic growth factors and cytokines to specific receptors triggers a cascade of intracellular events which results in cell proliferation and differentiation. The knowledge of ligand-receptor-signal pathways is not only important in understanding the pathophysiology of malignant disease but also essential for devising future therapeutic strategies. The advent of recombinant technology has made it possible to test the efficacy of selective differentiation therapy, and haemopoietic growth factors are undergoing clinical trials for a number of indications. In addition, increasingly the receptors for haemopoietic growth factors and cytokines have come under scientific scrutiny. Recently receptors for IL-2 alpha, IL-2 beta, IL-3, IL-4, IL-5, IL-6, IL-7, erythropoietin, G-CSF and GM-CSF have been isolated and cloned. It has become apparent that they have structural homology that is shared by receptors for growth hormone and prolactin, and this receptor group makes up the new cytokine receptor superfamily. The finding of sequence homology within these receptors suggests their evolutionary relationship. These receptors are transmembrane proteins 257-856 amino acids and their extracellular ligand-binding domain contains four conserved cysteine residues and a Trp-Ser-X-Trp-Ser motif. The secondary structure of the extracellular domain is made up of alpha-helices. High and low affinity binding forms exist for all these receptors. Binding affinity may depend on the formation of receptor heterodimers or multimers, association with other membrane proteins or differential glycosylation. Soluble receptor forms have been described for IL-2 alpha, IL-4, IL-5, IL-6 and IL-7. It is not known whether they are actively secreted or represent the degradation products of cell turnover. Their function may be to mop up excess cytokines and thereby confine the cytokine response. There is no sequence homology of the intracytoplasmic domains although several are rich in proline and serine residues, which may be important in mechanisms of signal transduction. No receptor in this superfamily functions as a receptor tyrosine kinase or has intrinsic protein tyrosine kinase activity. Detailed study of individual receptors holds clues to the regulation of receptor expression, ligand-receptor interactions and mechanisms involved in signal transduction. Such knowledge might explain the pleotropic effects cytokines may have on different cell types and their overlap in biological functions. Elevated levels of soluble IL-2 alpha receptor (Tac) are detected in hairy cell leukaemia, lymphomas and adult T-cell leukaemia (TL), and levels reflect tumour burden.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The cytokine receptor superfamily. 166 10


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